Low-frequency deflecting circuit



July 9, 1946.

T. T. EATON LOW FREQUENCY DEFLECTING CIRCUIT Filed Aug. so, 1943 AAAA AA /yaroe :.Snventor S'MA/ Gttorneg Patented July 9, 1946 OFFICE LOW-FREQUENCY DEFLECIING CIRCUIT Thomas 'T. Eaton, Haddon Heights, N.' J., assigner to Radio Corporation of America, a corporation of Delaware Application August 30. 1943, Serial No. $100,740'

6 Claims. (Cl. 175-335) My invention relates to electromagnetic deiiecting circuits and particularly to circuits for deflecting a cathode ray or the like at a very low repetition rate.

In apparatus where it is desired to deiiect a cathode ray at a very slow rate, such as a rate of one deection pe:l second, tor example, it is common practice to obtain the deiiecting voltage or current by mechanical means such as a potentiometer comprising current carrying resistor and a rotating potentiometer arm that makes a sliding contact with the resistor. This method of obtaining a sawtooth wave or the like for cathode ray deection has obvious disadvantages.

An o'fnect of the present invention is to provide an improved method oi.' and means for producing a 10W frequency deflecting current for electromagnetic deilection.

A further object of the invention is .to provide an improved method of and means for producing a low frequency deilecting current of sawtooth or triangular wave shape.

In one preferred embodiment of the invention. a sawtooth voltage wave is generated which recurs at the desired repetition rate and4 this voltage wave is applied to 'the control grid oi' a vacuum tube, such as a pentode, having high impedance between anode and ground. The anode circuit oi' the tube includes an anode resistor and a pair oi' deiiecting coils which have one terminal direct-current connected to the anode. 'I'he other terminal of the deecting coils is direct-current connected to a point that is at a steady potential which is lower than the anode supply potential. If, with a xed voltage (such as the average sawtooth voltage) on the control grid `oi.'

the tube, the resistance of the anode resistor' is adjusted until the anode potential equals said lower potential, the current now through the coils will then be zero. Any increase or decrease in the control grid voltage will cause ys. corresponding current iiow in the deiiecting coils in one direction or the other to produce the desired electromagnetic deflection.

The invention will be better understood from the following description taken in connectionl with the accompanying drawing in which the single ligure is a circuit diagram oi' one embodiment I3 is closed periodically for a motor driven cam i t. 'I'he saw tooth voltage it is applied through A a direct-current connection to the control grid Il of a high impedance vacuum tube suchas a pen- 'tode I8. The cathode It of the pentode may be connected to ground through a cathode resistor 2i. which introduces' some degeneration .for straightening the sawtooth curient wave. ".lhe value oi' the 4biasing voltage supplied by the battery il preferably is about equal to the cut-ofi voltage oi the tube i8, the capacitor-Il discharging substantially to this voltage while the switch nge is above the average value.

e I3 is closed.

A suitable anode voltage is applied to the anode 20 of tube I 0 through a variable anode resistor 22. One terminal oi' a pair o! detlecting coils `22 is directcurrent connected through a conductor 25 to the anode 20. The other terminal o! the coils 20 is direct-current connected to the junction point 2l of a resistor 28 and a glow tubev 21 that are serially connected across the anode voltage supply. The point 2l` is held at a constant potential by the glowv tube 21. For the purpose oi' illustration it is assumed that the anodey voltage is 300 y,volts andthatthe constant potential `at until the voltage drop'across resistor 22 is 150 volts. -There will now be no current ow through the deilecting coils 2l.

When the voltage wave I0 is applied to the grid il, with the circuit adjustedv as described above, a sawtooth current will flow through the coils 23; the .current flowing in one direction when the sawtooth lvoltage is below the average value, and in the opposite direction when the sawtooth volt- Centering may be accomplished lby .changing the adjustment ofthe resistor 22. It the resistor 22 hasia much larger resistance than the resistance of the denecting coils 2l, (the resistance o! the coils 22 being indicated at 22') the size or amplitude oi' the sawtooth deiiecting current will remain substantially unchanged with changes in the centering adjustment. In order to avoid wave shape distortion, the reactance of the deilecting coils 23 should be small compared'with the resistance of the snode'resistor 22.4 In the drawing. voltage-values have been'indicated merely by way o! example.

`a short interval by I I claim as my invention:

1. A low frequency deecting circuit comprising a vacuum tube having an anode. a cathode and a control grid, a direct-current voltage supply having a comparatively high potential point and a'n intermediate potential point, means for holding the voltage of said intermediate potential point constant regardless of the flow of deilecting current, said high potential point being connected to said anode through an anode resistor, a deecting coil that is connected between said anode and said intermediate potential point by direct-current connections only, means for producing a periodic voltage wave having a repetition rate equal to that of the desired low irequency deflection, and means for applying said voltage wave to said control grid to produce a periodic flow of anode current, said anode resistor having a, resistance such that the anode voltage equals the voltage of said intermediate potential point when the voltage on the control grid is at some intermediate value of said periodic voltage whereby denecting current flows through said ldeiiecting coil in one direction when the control grid voltage is less than said intermediate value and iiows through said coil in the opposite direction when the grid voltage is greater than said intermediate value.

2. A low frequency deilecting circuit comprising a vacuum tube having an anode. a cathode and a control grid and having high cathode-anode impedance, a direct-current voltage supply having a comparatively high potential point and an intermediate potential point, means for holding the voltage of said intermediate potential point constant regardless o! the ilow of deecting current, said high potential point being connected to said anode through a variable anode resistor, a deiiecting coll that is connected between said anode and said intermediate potential point by direct-current connections only, means fory producing a periodic voltage wave having a repetition rate equal to that of the desired low frequency deflection, and means for applying said voltage wave to said control grid to' produce a periodic ilow of anode current, said anode resistor having a resistance such that the anode voltage equals the voltage of said intermediate potential point when the voltage on the control grid is at some intermediate value of said periodic voltage whereby deiiecting current flows through said deecting coil in one direction when the control grid voltage is less than said intermediate value and ilows through said coil in the opposite direction when the grid voltage is greater than said intermediate value.

3. A low frequency deilecting circuit comprising a vacuum tube having an anode, a cathode and a control grid and having high cathode-anode impedance. a direct-current voltage supply having a comparatively high potential point and an intermediate potential point, means for holding the voltage of said intermediate potential point constant regardless of the ilow or deflecting current, said high potential point being connected to said anode through an anode resistor, a dedecting coil that is connected between said anode and said intermediate'potential point by direct-current connections only, means for producing a periodic voltage having a linear wave form and having a repetition rate equal to that of the desired low frequency deflection, and means for applying said voltage wave to said control grid to produce a periodic flow oi anode such that the anode voltage equals the voltage o! said intermediate potential point when the voltage on the control grid is at some intermediate value of said periodic voltage whereby deilecting current of linear wave form flows through said deilecting coil in one direction when the control grid voltage is less than said intermediate value and ows through said coil in the opposite direction when the grid voltage is greater than said intermediate value.

4. A low frequency deecting circuit comprising a vacuum tube having an` anode, a cathode and a control grid and having high cathode-anode impedance, a direct-current voltage supply having a comparatively high potential point and an intermediate potential pointmeans for holdin-g the voltage oi' said intermediate potential point constant regardless oi the ilow of deiiecting current, said high potential lpoint being connected to said anode through a variable anoderesistor, a deilectlng coil that is connected between said anode and said intermediate potential point by direct-current connections only, means iorproducing a. periodic voltagewave having a repetition rate equal to that of the desired low frequency deection, and means for applying said voltage wave to said control grid through a direct-current connection to produce a periodic ilow of anode current, said anode resistor having a resistance such that the anode voltage equals the voltage of said intermediate potential point when the voltage on the control grid is at some intermediate value of said periodic voltage whereby deecting said coil in the opposite direction when the grid voltage is greater than said intermediate value.

5. A low frequency deilecting circuit comprising@ deiiectlng coil. a vacuum tube having an anode, a cathode and a control grid and having high cathode-anode impedance compared with the impedance of said coila directcurrent voltage supply which `has a voltage divider connected thereacross. said voltage divider comprising a resistor and al constant voltage device connected in series with each other with the constant voltage device at the low potential end, said constant voltage device having the characteristic that the voltage thereacross is substantially independent of the current iiow therethrough within the operating range of the device, said anode being connected to the positive terminal oi' said voltage supply Athrough an anode resistor. -said deecting coil being conapplying said voltage. wave to said control grid to produce a periodic iiow oi' anode current. said anode resistor having a resistance such that the anode voltage equals the voltage at said Junction point when the voltage on thecontrol 4grid is at some intermediate value oi' said periodic voltage.'

whereby deiiecting current nows'through said deiiecting coil in one direction when the control' grid voltageis less than saidy intermediate value and iiows throughsaid coil in the opposite direction when the grid voltage is greater than said intermediate value.

6. A low frequency de'ectlng circuit' com` curreut, said anode resistor having a resistance 76 prising a deiiecting coil, a vacuumtube having 5v an anode, a cathode and 'a control grid anld.' having high cathode-anode impedance compared with the impedance of said coil, a directcurrent voltage supply which has a voltage divider connected thereacross, said voltage divider comprising a resistor and a glow tube connected in series with each other with the glow equal to that -of the-desired low frequency deflection, and meansfor applying said voltage wave to said control grid'through a direct-current connection to produce a periodic iiow of anode current, said anode resistor having a resistance such that the anode voltage equals the voltage at said junction point when the voltage on the control grid is at some intermediate value of said periodic voltage whereby defiecting current flows through said deecting coil in one direction when the control grid voltage is less than said intermediate value and flows throughvsaid coil in the opposite direction when the grid voltage is greater than said intermediate value.l

'THOMAS T. EATON. 

